The invention concerns a process for reactivation of honeycomb-constructed catalyst elements for the denitrification of flue gases from fossil fired boiler facilities, especially coal-fired major power plant boiler facilities.
Flue gases from fossil-fired boiler facilities, especially from coal-fired major power plant boiler facilities, must be subjected to a comprehensive cleansing, that is primarily to a dust removal process, desulfurization and denitrification, for reasons of environmental protection.
In this connection, at least in the power plant area, denitrification is usually conducted first, then dust removal is carried out by means of an electrostatic precipitator, and finally desulfurization is implemented in a wet washer by a reaction of the SO42xe2x88x92 ions with Ca2+ ions to CaSO4.
The denitrification of flue gas takes place at temperatures between about 300-400xc2x0 C. by a reaction of nitrogen oxides (NOx) with ammonia to molecular nitrogen and water.
For attaining a satisfactory rate and degree of transformation, it is indispensable to support the denitrification reaction by suitable catalysts.
For example, the denitrification reactor incorporated into the 770 MW Bexbach bituminous coal power plant operated by the applicant consists of four catalyst levels which are outfitted with a total of three catalyst layers. Each catalyst layer once again consists of a number of individual catalytic elements in the order of magnitude of about 1.4 m high, 2.5 m wide and 1.15 m deep. These catalytic elements are constructed in the form of a honeycomb with a cross section area of about 10 mm2 per honeycomb. In the Bexbach power plant, titanium dioxide-based tungsten-containing catalysts with a further active component, vanadium pentoxide, are in use. For improving the mechanical loading capacity of the elements, calcium-aluminum silicate support fibers are admixed to the titanium dioxide-containing groundmass.
It has become evident in operating the Bexbach power plant that the activity of the catalytic elements has already declined greatly after about twenty thousand operating hours. In addition to the lowered reduction of the nitrogen oxides, an activity diminished in this way leads to increased ammonia slippage, that is, the flue gas leaving the denitrification reactor still contains noticeable amounts of ammonia, which can lead to contamination due to the formation of ammonia salts, as well as to pollution of the fly ash in facility elements connected at the output end, for example in the air heater.
To date, it has therefore been the usual practice to replace used catalytic elements whose activity has declined to a third of the original activity by new ones, or retroactively to provide a further layer of new catalytic elements. Considerable costs arise for power plant operators through reoutfitting, in addition to problems with the elimination of used elements. For example, at present the reoutfitting of a level in the reactor of the Bexbach power plant costs about 6 million DM.
Underlying invention is thus the object of developing a process through which used catalytic elements can be reactivated and consequently be reused for flue gas denitrification.